The present invention relates to a high pressure fuel pump for force-feeding high pressure fuel to a fuel injection valve of an internal combustion engine.
An apparatus in the past had a rubber seal structure as structure for sealing an outer wall of a plunger to be fluid-tight as disclosed in JP-A-8-68370 specification. In addition, a fuel reservoir formed on a pressurization chamber side of the seal structure was communicated with a passage having pressure equal to atmospheric pressure so as to be opened to the atmospheric pressure.
However, such a high pressure fuel pump in the past requires a clearance of several μm to several tens of μm between a cylinder inner wall and a plunger outer wall for the sake of plunger sliding. Upon fuel injection, if fuel in a fuel pressurization chamber is pressurized, the fuel leaks from the clearance, so that the same pressure as a suction pressure is also applied to the fuel reservoir. In the case of using a rubber lip seal as the seal structure, there was a problem that a limit value of resistance to pressure is too low to withstand the suction pressure, so that seal performance is deteriorated.
In order to solve such a problem, an apparatus according to JP-A-8-68370 specification has the fuel reservoir in communication with to the passage having the pressure equal to atmospheric pressure, but to that end, leaked fuel must be returned to a fuel tank and so piping for tank return must be provided. For that reason, there were problems such as increase in working man-hours and increased costs.
In addition, there was a problem that usable materials are limited due to formability of the lip seal, and seal performance deteriorates since its rigidity is extremely reduced by the fuel including alcohol and so on resulting in little allowance.
An object of the present invention is to provide a high pressure fuel pump for an internal combustion engine of low costs and high reliability implemented to solve the above problems.